Mobility synchronization measurements

ABSTRACT

There is provided a method for handling mobility synchronization measurements. The method is performed by a wireless device. The method comprises receiving an indication to perform mobility measurements on a set of transmission beams associated with a unique identity. The method comprises checking if the unique identity has previously been stored by the wireless device. The method comprises, if the unique identity has not previously been stored by the wireless device, performing mobility measurements on the set of transmission beams to determine synchronization information of the set of transmission beams. The method comprises storing the unique identity and the synchronization information of the mobility measurements.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. application Ser. No.15/517,446 filed Apr. 6, 2017 (371(c) date), which is a 35 U.S.C. § 371national stage of international application PCT/EP2014/071537 filed Oct.8, 2014. All of these earlier applications are hereby incorporatedherein by reference in their entireties.

TECHNICAL FIELD

Embodiments presented herein relate to handling mobility synchronizationmeasurements, and particularly to methods, a wireless device, a radioaccess network node, computer programs, and a computer program productfor handling mobility synchronization measurements.

BACKGROUND

In communications networks, there may be a challenge to obtain goodperformance and capacity for a given communications protocol, itsparameters and the physical environment in which the communicationsnetwork is deployed.

For example, handover is a vital part of any cellular communicationsnetwork. A handover may be defined as the process of transferring anongoing connection of a wireless device from one radio access networknode (denoted the serving radio access network node) to another radioaccess network node (denoted the target radio access network node) inorder to accomplish a transparent service over a large coverage area.The handover should be performed without any loss of data transmissionto/from the wireless device, and with as small interrupt as possible forthe wireless device.

To enable a handover, it is necessary to find a suitable target cell asserved by the target radio access network node, and to ensure that it ispossible to sustain reliable communication to/from the wireless devicein the target cell. Candidates for suitable target radio access networknodes (and/or target cells) are usually stored in so-called neighborlists, which are stored at least at the serving radio access networknode.

For a wireless device (WD) to receive or measure on a target cell (i.e.,an area served by a target radio access network (RAN) node), it needs besynchronized with the cell (i.e., with the target node). In legacysystems, all RAN nodes continuously transmit synchronization signalsthat WDs in neighbor cells use for synchronization with target cell.Examples include, but are not limited to, the synchronization channel(SCH) in Wideband Code Division Multiple Access (WCDMA) basedcommunications networks and the primary and secondary synchronizationsignals in Long Term Evolution (LTE) based communications networks. Thesynchronization is usually achieved by correlating the received signalwith a known signal; in LTE the correlation may be performed in bothtime and frequency domain. The synchronization procedure is often divedinto several steps where the frequency and time resolution and isimproved for each step. For time synchronization, the steps may includefinding symbol, slot and frame timing.

Future cellular communications networks may use advanced antenna systemsto a large extent. With such antennas, signals will be transmitted innarrow transmission beams to increase signal strength in somedirections, and/or to reduce interference in other directions. When theantenna is used to increase coverage, handover between narrowtransmission beams in neighboring RAN nodes may become a necessity. Theserving RAN node also needs to decide if a beam switch or beam update isnecessary within the own cell. The transmission beam through which theRAN node is currently communicating with the WD is called the servingbeam and the transmission beam it will hand over to, or switch to, iscalled the target beam. The serving beam and the target beam may betransmission beams of the same or different RAN node.

In a cellular system with an advanced antenna system that uses narrowbeams, beam updates for a WD might recur quite often. To synchronize andmeasure on the different candidate beams, the WD) must thus potentiallyperform extensive timing synchronization procedures, especially innon-synchronized networks. For the WD, the synchronization procedure maybe quite complex, since it may need to measure on many transmissionbeams at once.

Hence, there is still a need for improved handling of mobilitysynchronization measurements.

SUMMARY

An object of embodiments herein is to provide efficient handling ofmobility synchronization measurements.

According to a first aspect there is presented a method for handlingmobility synchronization measurements. The method is performed by awireless device. The method comprises receiving an indication to performmobility measurements on a set of transmission beams associated with aunique identity. The method comprises checking if the unique identityhas previously been stored by the wireless device. The method comprises,if the unique identity has previously been stored by the wirelessdevice, performing mobility measurements on the set of transmissionbeams based on previously stored synchronization information of the setof transmission beams, wherein the synchronization information isidentified by the unique identity.

Advantageously this provides efficient handling of mobilitysynchronization measurements.

Advantageously this enables the time it takes for the WD to acquiresynchronization to a target beam to be reduced compared to traditionalapproaches.

Advantageously, this enables the complete synchronization process to beperformed less frequently compared to traditional approaches. Runningthe complete synchronization process less frequently will save WDcomplexity.

According to a variation of the first aspect there is presented a methodfor handling mobility synchronization measurements. The method isperformed by a wireless device. The method comprises receiving anindication to perform mobility measurements on a set of transmissionbeams associated with a unique identity. The method comprises checkingif the unique identity has previously been stored by the wirelessdevice. The method comprises, if the unique identity has not previouslybeen stored by the wireless device, performing mobility measurements onthe set of transmission beams to determine synchronization informationof the set of transmission beams. The method comprises storing theunique identity and the synchronization information of the mobilitymeasurements.

According to a second aspect there is presented a wireless device forhandling mobility synchronization measurements. The wireless devicecomprises a processing unit. The processing unit is configured toreceive an indication to perform mobility measurements on a set oftransmission beams associated with a unique identity. The processingunit is configured to check if the unique identity has previously beenstored by the wireless device. The processing unit is configured to, ifthe unique identity has previously been stored by the wireless device,perform mobility measurements on the set of transmission beams based onpreviously stored synchronization information of the set of transmissionbeams, wherein the synchronization information is identified by theunique identity.

According to a variation of the second aspect there is presented awireless device for handling mobility synchronization measurements. Thewireless device comprises a processing unit. The processing unit isconfigured to receive an indication to perform mobility measurements ona set of transmission beams associated with a unique identity. Theprocessing unit is configured to check if the unique identity haspreviously been stored by the wireless device. The processing unit isconfigured to, if the unique identity has not previously been stored bythe wireless device, perform mobility measurements on the set oftransmission beams to determine synchronization information of the setof transmission beams. The processing unit is configured to store theunique identity and the synchronization information of the mobilitymeasurements

According to a third aspect there is presented a computer program forhandling mobility synchronization measurements, the computer programcomprising computer program code which, when run on a processing unit ofa wireless device, causes the processing unit to perform a methodaccording to at least one of the first aspect and the variation of thefirst aspect.

According to a fourth aspect there is presented a method for handlingmobility synchronization measurements. The method is performed by aradio access network node. The method comprises transmitting anindication for a wireless device to perform mobility measurements on aset of transmission beams associated with a unique identity.

According to a fifth aspect there is presented a radio access networknode for handling mobility synchronization measurements. The radioaccess network node comprises a processing unit. The processing unit isconfigured to transmit an indication for a wireless device to performmobility measurements on a set of transmission beams associated with aunique identity.

According to a sixth aspect there is presented a computer program forhandling mobility synchronization measurements, the computer programcomprising computer program code which, when run on a processing unit ofa radio access network node, causes the processing unit to perform amethod according to the fourth aspect.

According to a seventh aspect there is presented a computer programproduct comprising a computer program according to at least one of thethird aspect and the sixth aspect and a computer readable means on whichthe computer program is stored.

It is to be noted that any feature of the first, second, third, fourth,fifth, sixth and seventh aspects may be applied to any other aspect,wherever appropriate. Likewise, any advantage of the first aspect mayequally apply to the second, third, fourth, fifth, sixth and/or seventhaspect, respectively, and vice versa. Other objectives, features andadvantages of the enclosed embodiments will be apparent from thefollowing detailed disclosure, from the attached dependent claims aswell as from the drawings.

Generally, all terms used in the claims are to be interpreted accordingto their ordinary meaning in the technical field, unless explicitlydefined otherwise herein. All references to “a/an/the element,apparatus, component, means, step, etc.” are to be interpreted openly asreferring to at least one instance of the element, apparatus, component,means, step, etc., unless explicitly stated otherwise. The steps of anymethod disclosed herein do not have to be performed in the exact orderdisclosed, unless explicitly stated.

BRIEF DESCRIPTION OF THE DRAWINGS

The inventive concept is now described, by way of example, withreference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram illustrating a communications networkaccording to embodiments;

FIG. 2a is a schematic diagram showing functional units of a radioaccess network node according to an embodiment:

FIG. 2b is a schematic diagram showing functional modules of a radioaccess network node according to an embodiment;

FIG. 3a is a schematic diagram showing functional units of a wirelessdevice according to an embodiment;

FIG. 3b is a schematic diagram showing functional modules of a wirelessdevice according to an embodiment;

FIG. 4 shows one example of a computer program product comprisingcomputer readable means according to an embodiment;

FIGS. 5, 6, 7, and 8 are flowcharts of methods according to embodiments.

DETAILED DESCRIPTION

The inventive concept will now be described more fully hereinafter withreference to the accompanying drawings, in which certain embodiments ofthe inventive concept are shown. This inventive concept may, however, beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein; rather, these embodiments areprovided by way of example so that this disclosure will be thorough andcomplete, and will fully convey the scope of the inventive concept tothose skilled in the art. Like numbers refer to like elements throughoutthe description. Any step or feature illustrated by dashed lines shouldbe regarded as optional.

FIG. 1 is a schematic diagram illustrating a communications network towhere embodiments presented herein can be applied. The communicationsnetwork 10 comprises radio access network (RAN) nodes 11 a, 11 b. EachRAN node may have a transmission point, one of which is schematicallyillustrated at reference numeral 11 c. The RAN nodes may be anycombination of radio base stations such as base transceiver stations,node Bs, and/or evolved node Bs. The RAN nodes may further be anycombination of macro RAN nodes and micro, or pico, RAN nodes. Each RANnode 11 a, 11 b provides network coverage in a respective coverageregion 12 a, 12 b by transmitting transmission beams 15 a, 15 b, 15 c,15 d, 15 f in that coverage region 12 a, 12 b. Each RAN node 11 a, 11 bis assumed to be operatively connected to a core network (notillustrated). The core network may in turn be operatively connected to aservice and data providing wide area network.

Hence, a wireless device (WD) 13 served by one of the RAN nodes 11 a, 11b may thereby access services and data as provided by the wide areanetwork. The wireless devices 13 may be any combination of mobilestations, mobile phones, handsets, wireless local loop phones, userequipment (UE), smartphones, laptop computers, and/or tablet computers.Each wireless device 13 is located at current position [x1, y1]according to some coordinate system [x, y]. Further, although only twocoordinates x and y are schematically illustrated in FIG. 1, the currentposition may have three coordinates [x1, y1, z1] for wireless device 13in a three-dimensional coordinate system [x, y, z].

A wireless device 13 may move from position to position and thus fromcoverage region to 12 a, 12 b thus requiring handover of the wirelessdevice 13 from one RAN node to another RAN node, or at least from onetransmission beam to another transmission beam. As noted above, suchhandover should be performed without any loss of data transmissionto/from the wireless device 13 and with as small interrupt as possiblefor the wireless device 13. The serving beam and the target beam may betransmission beams of the same or different RAN node. Hence, the termhandover as herein used should be interpreted as a handover from asource beam to a target beam.

For illustrative, non-limiting, purposes it is in FIG. 1 assumed thatthe WD 13 is currently positioned at the border of two regions 12 a, 12b. For illustrative, non-limiting, purposes it is in FIG. 1 furtherassumed that RAN node 11 a is the serving RAN node and the RAN node 11 bis the target RAN node. Each RAN node 11 a, 11 b is equipped withantennas configured to generate narrow transmission beams 15 a, 15 b, 15c, 15 d, 15 f. For illustrative, non-limiting, purposes it is in FIG. 1assumed that transmission beam 15 a is the serving beam for WD 13 andthe other transmission beams 15 b-15 f are candidate target beams.

As noted above, in a cellular system, such as in the communicationsnetwork to, with RAN nodes 11 a, 11 b having advanced antenna systemsthat uses narrow transmission beams 15 a-f, beam updates for a WD 13might recur quite often. To synchronize and measure on the differentcandidate beams, the WD must thus, according to prior art, potentiallyperform extensive timing synchronization procedures, especially innon-synchronized networks. For the WD 13, the synchronization procedureaccording to prior art may thus be quite complex, since it may need tomeasure on many transmission beams 15 a-f at once. There is thus a needfor a candidate beam measurement approach where mobility measurementcomputational load at the WD 13 is minimized, or at least reduced.

The embodiments disclosed herein relate to handling of mobilitysynchronization measurements. In order to obtain such handling ofmobility synchronization measurements there is provided a wirelessdevice 13, a method performed by the wireless device 13, a computerprogram comprising code, for example in the form of a computer programproduct, that when run on a processing unit of the wireless device 13,causes the processing unit to perform the method of the wireless device13. In order to obtain such handling of mobility synchronizationmeasurements there is further provided a RAN node 11 a, 11 b, a methodperformed by the RAN node 11 a, 11 b, a computer program comprisingcode, for example in the form of a computer program product, that whenrun on a processing unit of the RAN node 11 a, 11 b, causes theprocessing unit to perform the method.

FIG. 2a schematically illustrates, in terms of a number of functionalunits, the components of a RAN node 11 a, 11 b according to anembodiment. A processing unit 21 is provided using any combination ofone or more of a suitable central processing unit (CPU), multiprocessor,microcontroller, digital signal processor (DSP), application specificintegrated circuit (ASIC), field programmable gate arrays (FPGA) etc.,capable of executing software instructions stored in a computer programproduct 41 a (as in FIG. 4), e.g. in the form of a storage medium 23.Thus the processing unit 21 is thereby arranged to execute methods asherein disclosed. The storage medium 23 may also comprise persistentstorage, which, for example, can be any single one or combination ofmagnetic memory, optical memory, solid state memory or even remotelymounted memory. The RAN node 11 a, 11 b may further comprise acommunications interface 22 for communications with other radio accessnetwork nodes 11 a, 11 b and wireless devices 13. As such thecommunications interface 22 may comprise one or more transmitters andreceivers, comprising analogue and digital components and a suitablenumber of antennas for radio communications anti ports for wiredcommunications. The processing unit 21 controls the general operation ofthe RAN node 11 a, 11 b e.g. by sending data and control signals to thecommunications interface 22 and the storage medium 23, by receiving dataand reports from the communications interface 22, and by retrieving dataand instructions from the storage medium 23. Other components, as wellas the related functionality, of the RAN node 11 a, 11 b are omitted inorder not to obscure the concepts presented herein.

FIG. 2b schematically illustrates, in terms of a number of functionalmodules, the components of a RAN node 11 a, 11 b according to anembodiment. The RAN node 11 a, 11 b of FIG. 2b comprises a number offunctional modules such as a send and/or receive module 21 a configuredto perform below step S202, S204 a, S204 b, S204 c, S208, S212, S214.The RAN node 11 a, 11 b of FIG. 2b may further comprises a number ofoptional functional modules, such as any of an identify module 21 bconfigured to perform below step S206, and a determine module 21 cconfigured to perform below step S210. The functionality of eachfunctional module 21 a-c will be further disclosed below in the contextof which the functional modules 21 a-c may be used. In general terms,each functional module 21 a-c may be implemented in hardware or insoftware. Preferably, one or more or all functional modules 21 a-c maybe implemented by the processing unit 21, possibly in cooperation withfunctional units 22 and/or 23. The processing unit 21 may thus bearranged to from the storage medium 23 fetch instructions as provided bya functional module 21 a-c and to execute these instructions, therebyperforming any steps as will be disclosed hereinafter.

FIG. 3a schematically illustrates, in terms of a number of functionalunits, the components of a wireless device 13 according to anembodiment. A processing unit 31 is provided using any combination ofone or more of a suitable central processing unit (CPU), multiprocessor,microcontroller, digital signal processor (DSP), application specificintegrated circuit (ASIC), field programmable gate arrays (FPGA) etc.,capable of executing software instructions stored in a computer programproduct 41 b (as in FIG. 4), e.g. in the form of a storage medium 33.Thus the processing unit 31 is thereby arranged to execute methods asherein disclosed. The storage medium 33 may also comprise persistentstorage, which, for example, can be any single one or combination ofmagnetic memory, optical memory, solid state memory or even remotelymounted memory. The wireless device 13 may further comprise acommunications interface 32 for communications with at least one RANnode 11 a, 11 b. As such the communications interface 32 may compriseone or more transmitters and receivers, comprising analogue and digitalcomponents and a suitable number of antennas for radio communications.The processing unit 31 controls the general operation of the wirelessdevice 13 e.g. by sending data and control signals to the communicationsinterface 32 and the storage medium 33, by receiving data and reportsfrom the communications interface 32, and by retrieving data andinstructions from the storage medium 33. Other components, as well asthe related functionality, of the wireless device 13 are omitted inorder not to obscure the concepts presented herein.

FIG. 3b schematically illustrates, in terms of a number of functionalmodules, the components of a wireless device 13 according to anembodiment. The wireless device 13 of FIG. 3b comprises a number offunctional modules; a send and/or receive module 31 a configured toperform below steps S102, S110 a, S112, S114, S120, a check module 31 bconfigured to perform below steps S114, S116, and a perform module 31 econfigured to perform below steps S106 a, S106 b, S106 c. The wirelessdevice 13 of FIG. 3b may further comprises a number of optionalfunctional modules, such as any of a store module 31 d configured toperform below step S108, a retrieve module 31 e configured to performbelow step S118, and an update module 31 e configured to perform belowstep Snob. The functionality of each functional module 31 a-e will befurther disclosed below in the context of which the functional modules31 a-e may be used. In general terms, each functional module 31 a-e maybe implemented in hardware or in software. Preferably, one or more orall functional modules 31 a-e may be implemented by the processing unit21, possibly in cooperation with functional units 22 and/or 23. Theprocessing unit 21 may thus be arranged to from the storage medium 23fetch instructions as provided by a functional module 31 a-e and toexecute these instructions, thereby performing any steps as will bedisclosed hereinafter.

FIG. 4 shows one example of a computer program product 41 a, 41 bcomprising computer readable means 43. On this computer readable means43, a computer program 42 a can be stored, which computer program 42 acan cause the processing unit 21 and thereto operatively coupledentities and devices, such as the communications interface 22 and thestorage medium 23, to execute methods according to embodiments describedherein. On this computer readable means 43, a computer program 42 b canbe stored, which computer program 42 b can cause the processing unit 31and thereto operatively coupled entities and devices, such as thecommunications interface 32 and the storage medium 33, to executemethods according to embodiments described herein. The computer programs42 a, 42 b and/or computer program product 41 a, 41 b may thus providemeans for performing any steps as herein disclosed.

In the example of FIG. 4, the computer program product 41 a, 41 b isillustrated as an optical disc, such as a CD (compact disc) or a DVD(digital versatile disc) or a Blu-Ray disc. The computer program product41 a, 41 b could also be embodied as a memory, such as a random accessmemory (RAM), a read-only memory (ROM), an erasable programmableread-only memory (EPROM), or an electrically erasable programmableread-only memory (EEPROM) and more particularly as a non-volatilestorage medium of a device in an external memory such as a USB(Universal Serial Bus) memory or a Flash memory, such as a compact Flashmemory. Thus, while the computer program 41 a, 41 b is hereschematically shown as a track on the depicted optical disk, thecomputer program 42 a, 42 b can be stored in any way which is suitablefor the computer program product 41 a, 41 b.

FIGS. 5 and 6 are flow chart illustrating embodiments of methods forhandling mobility synchronization measurements as performed by thewireless device 13. The methods are advantageously provided as computerprograms 42 b. FIGS. 7 and 8 are flow chart illustrating embodiments ofmethods for handling mobility synchronization measurements as performedby the RAN node 11 a. The methods are advantageously provided ascomputer programs 42 a.

Reference is now made to FIG. 5 illustrating a method for handlingmobility synchronization measurements as performed by the wirelessdevice 13 according to an embodiment.

The wireless device 13 is configured to, in a step S102, receive anindication to perform mobility measurements on a set of transmissionbeams 15 a, 15 b, 15 c, 15 d, 15 e, 15 f. The set of transmission beams15 a, 15 b, 15 c, 15 d, 15 e, 15 f is associated with a unique identity.Examples of the unique identity will be provided below.

Once having received this indication the wireless device 13 does notimmediately perform mobility measurements on the set of transmissionbeams 15 a, 15 b, 15 c, 15 d, 15 e, 15 f. Instead, the wireless device13 is configured to, in a step S104, check if the unique identity haspreviously been stored by the wireless device 13.

If the unique identity has previously been stored by the wireless device13 this may indicate that previous information may be used to assistwhen performing the mobility measurements on the set of transmissionbeams 15 a, 15 b, 15 c, 15 d, 15 e, 15 f. Particularly, the wirelessdevice 13 is configured to, in a step S106 a, if the unique identity haspreviously been stored by the wireless device 13, perform mobilitymeasurements on the set of transmission beams 15 a, 15 b, 15 c, 15 d, 15e, 15 f. The mobility measurements are based on previously storedsynchronization information of the set of transmission beams 15 a, 15 b,15 c, 15 d, 15 e, 15 f. The synchronization information is identified bythe unique identity.

Embodiments relating to further details of handling mobilitysynchronization measurements as performed by the wireless device 13 willnow be disclosed.

The unique identity may also identify the transmitting RAN node 11 a, 11b and/or transmission point 11 c. In this way future measurement oncandidate beams from the same RAN node can take advantage of the samestored synchronization information. Hence, the unique identity mayidentify the RAN node 11 a and/or the transmission point 11 c from whichthe set of transmission beams 15 a, 15 b, 15 c, 15 d, 15 e, 15 f wastransmitted.

There may be different ways to provide the unique identity. For example,the unique identity may be represented by a sequence of binary digits.Identities of single transmission beams 15 a, 15 b, 15 c, 15 d, 15 e, 15f in the set of transmission beams may share at least a subset of thesequence of binary digits. Hence, the wireless device 13 does not needto perform mobility measurements on such transmission beams that do notshare such at least subset of the sequence of binary digits. That is,since the wireless device 13 thereby only performs mobility measurementson transmission beams that share the unique identity, the wirelessdevice 13 does not need to perform unnecessary mobility measurements onother transmission beams. The subset of the sequence of binary digitsmay correspond to an identity of a RAN node 11 a, 11 b. However, thesubset of the sequence of binary digits may alternatively correspond toan identity of a group of RAN nodes, or a subset of transmission beamsof one RAN node.

There may be different ways for the wireless device 13 to receive thesynchronization information. For example, the synchronizationinformation may be determined from synchronization signals transmittedin the set of transmission beams 15 a, 15 b, 15 c, 15 d, 15 e, 15 f.

There may be different types of synchronization information. In generalterms, the synchronization information may be any combination of timesynchronization information and frequency synchronization information.For example, the synchronization information may comprise a time offsetto start of a first symbol of a first frame relative an internal clockof the wireless device 13. For example, the synchronization informationmay comprise a frequency offset to relative a reference frequency usedby the wireless device 13. Both the WD clock and frequency reference maybe assumed to be locked to the current serving beam. Alternatively,timing and frequency of the serving RAN node 11 a become the internalreferences.

The wireless device 13 may then use the synchronization information toimprove the measurements the next time it is requested to measuresynchronization information, such as time synchronization signals (TSS)and/or mobility reference signals (MRS), sent on the same transmissionbeam.

The mobility measurements may further be based on reference signalstransmitted in the set of transmission beams 15 a, 15 b, 15 c, 15 d, 15e, 15 f.

Reference is now made to FIG. 6 illustrating methods for handlingmobility synchronization measurements as performed by the wirelessdevice 13 according to further embodiments.

There may be different ways for the wireless device 13 to act if theunique identity has not previously been stored by the wireless device13. For example, the wireless device 13 may perform new mobilitymeasurements, and then store the unique identity and synchronizationinformation.

Particularly, the wireless device 13 may be configured to, in anoptional step S106 b, if the unique identity has not previously beenstored by the wireless device 13, perform mobility measurements on theset of transmission beams 15 a, 15 b, 15 c, 15 d, 15 e, 15 f todetermine synchronization information of the set of transmission beams15 a, 15 b, 15 c, 15 d, 15 e, 15 f. The wireless device 13 may then beconfigured to, in an optional step S108, store the unique identity andthe synchronization information of the mobility measurements.

For example, after the wireless device 13 has performed successfulmeasurements on a transmission beam's TSS and/or MRS, the wirelessdevice 13 may store the synchronization parameters in a lookup table. Ingeneral terms, by a successful measurement is meant that one or morecorrelation metrics used for synchronization are above some respectivethreshold values.

As noted above, the unique identity may also identify the transmittingRAN node 11 a, 11 b and/or transmission point 11 c defining a cell ID.Hence, in one embodiment, such a table may be indexed using beam ID andcell ID, see Table 1.

TABLE 1 Example of a synchronization table used for a WD to look up timeand frequency synchronization parameters for a cell and beam. Timesynch. Frequency synch. Cell ID/Beam ID parameters parameters A, 1 t₁ f₁A, 2 t₂ f₂ B, 1 t₃ f₃ . . . . . . . . .

Hence, at least some of the herein disclosed embodiments are based onusing an association of each transmission beam with a unique beam IDindex. The communications network to may, via a RAN node 11 a, informthe WD 13 about the beam ID when requesting mobility measurements on thetransmission beam. When the WD 13 has identified the transmission beamand performed synchronization, the WD 13 may store the synchronizationinformation (inter alia comprising settings) for the transmission beamusing the beam ID. The stored settings may then be used by the WD 13 thenext time the WD 13 is requested to perform mobility measurements on thetransmission beam.

In practice Table 1 may be stored as a lookup table. Such a lookup tablewill have limited size and only the transmission beams for the N latestmeasured cells (RAN nodes) will be stored. It may be useful to have aseparate table that only stores the time synchronization parameter forthe cells (RAN nodes), see Table 2. Out of all synchronizationparameters, the timing synchronization offset is the one that has thepotential to reduce the WD processing load the most. The number oftransmission beams per cell (RAN node) may be in the order 10-100. Table2 will be able to store time parameters for a larger number of cells(RAN nodes) for the same memory size as for storing Table 1. The timesynchronization parameter for a cell (RAN node) could be the averagevalue for all the measured transmission beams for the cell (RAN node).The time synchronization parameter may be used for the initial timesynchronization for a transmission beam from a cell (RAN node) that isonly included in Table 2.

TABLE 2 An example of a synchronization table used for a WD to look upthe time synchronization parameters for a cell. Time synchronizationCell ID parameters A t₁ B t₂ C t₃ . . . . . .

Further, if a transmission beam is sent from a RAN node that is includedin the table, even if the specific transmission beam has not beenencountered previously, the synchronization parameters for the othertransmission beams from that same RAN node could be used as initialparameters. Stored synchronization information of other transmissionbeams may thus be used to as initial parameters. Particularly, thewireless device 13 may be configured to, in an optional step S106 c, ifthe unique identity has not previously been stored by the wirelessdevice 13, perform mobility measurements on the set of transmissionbeams 15 a, 15 b, 15 c, 15 d, 15 e, 15 f to determine synchronizationinformation of the set of transmission beams 15 a, 15 b, 15 c, 15 d, 15e, 15 f. The mobility measurements are based on previously storedsynchronization information of another set of transmission beams. Thepreviously stored synchronization information is identified by a uniqueidentity of this another set of transmission beams. Further, thepreviously stored synchronization information of this another set oftransmission beams may be used to define initial parameters to be usedduring the mobility measurements on the set of transmission beams 15 a,15 b, 15 c, 15 d, 15 e, 15 f.

There may be different ways to update previously stored synchronizationinformation. For example, previously stored synchronization informationmay be updated when the wireless device 13 is in idle mode.Particularly, the wireless device 13 may be configured to, in anoptional step S110 a, receive, while in idle mode, broadcastedinformation, such as, but not limited to, synchronization information.The wireless device 13 may then be configured to, in an optional stepS110 b update previously stored synchronization information based on thebroadcasted information. Table 2 may thus also be updated in idle mode,using synchronization and reference signals that are broadcasted in acell. These synchronization and reference signals are generally sent tooinfrequently to be useful in active mode. A WD 13 is in active mode whenit receives or transmits data.

There may be different ways for the wireless device 13 to handle themobility measurements. For example, the wireless device 13 may informthe RAN node 11 a, 11 b of the mobility measurements. Particularly, thewireless device 13 may be configured to, in an optional step S112,transmit information of the mobility measurements to a RAN node. ThisRAN node may be the serving RAN node 11 a of the wireless device 13 or atarget RAN node, such as the RAN node 11 b, of the wireless device 13.The wireless device 13 may thus inform the RAN node about gatheredinformation about per-beam or pre-node synchronization parameters. TheRAN node may then omit sending e.g. the TSS component in subsequentmeasurement session using previously activated transmission beams, RANnodes, or transmission points.

The mobility measurements may be used to determine whether the wirelessdevice 13 should be handed over from a serving RAN node, such as the RANnode 11 a, to a target RAN node, such as the RAN node 11 b. However, asnoted above, handover should in this context have a broad interpretationand may comprise handover from a serving beam to a target beam, wherethe serving beam and the target beam are transmitted from the same RANnode 11 a, 11 b. Particularly, the wireless device 13 may be configuredto, in an optional step S114, receive a beam switch command from a RANnode 11 a serving the wireless device 13. The beam switch commandcomprises a target beam identity. The wireless device 13 may then beconfigured to, in an optional step S116, check if the target beamidentity corresponds to any unique identity that has previously beenstored by the wireless device 13. The wireless device 13 may then beconfigured to, in an optional step S118, retrieve stored synchronizationinformation corresponding to the unique identity if the target beamidentity corresponds to any unique identity that has previously beenstored by the wireless device 13. The wireless device 13 may then beconfigured to, in an optional step S120, receive data transmission usingthe retrieved synchronization information.

Reference is now made to FIG. 7 illustrating a method for handlingmobility synchronization measurements as performed by the RAN node 11 aaccording to an embodiment.

As disclosed above the wireless device 13 in step S102 receives anindication to perform mobility measurements. Hence the RAN node 11 a isconfigured to, in a step S202, transmit an indication for the wirelessdevice 13 to perform mobility measurements on the set of transmissionbeams 15 a, 15 b, 15 c, 15 d, 15 e, 15 f associated with the uniqueidentity.

Embodiments relating to further details of handling mobilitysynchronization measurements as performed by the RAN node 11 a will nowbe disclosed.

Reference is now made to FIG. 8 illustrating methods for handlingmobility synchronization measurements as performed by the RAN node 11 aaccording to further embodiments.

There may be different ways for the RAN node 11 a to act once it hastransmitted the indication in step S202. Different embodiments relatingthereto will now be described in turn.

For example, the RAN node 11 a may be configured to, in an optional stepS204 a, transmit synchronization information using the set oftransmission beams associated with the unique identity. Thissynchronization information may be received by the wireless device 13 asin step S110 a.

For example, the RAN node 11 a may be configured to, in an optional stepS204 b, transmit a message to another RAN node 11 b to activatetransmission of synchronization information using the set oftransmission beams 15 a, 15 b, 15 c, 15 d, 15 e, 15 f associated withthe unique identity. This may be the case if the RAN node 11 a hasidentified a need for a beam switch, see step S206 below.

For example, the RAN node 11 a may be configured to, in an optional stepS204 c, transmit a message to another RAN node 11 b. The message maycomprise position information [x1, y1] of the wireless device 13. Thismay enable this another RAN node 11 b to choose which transmission beamsto active for transmission towards the wireless device 13.

Further, the RAN node 11 a may be configured to, in an optional stepS206, identify that a beam switch is needed for the wireless device 13.The set of transmission beams may then be based thereon. Hence, whichbeams to be included in the set of transmission beams may be based onwhether a beam switch is needed for the wireless device 13 or not. Theset of transmission beams may then represent candidate target beams forthe wireless device 13.

There may be different ways for the RAN node 11 a to determine whichtransmission beam is to be used as the new serving beam of the WD 13.Particularly, the RAN node 11 a may be configured to, in an optionalstep S208, receive information of the mobility measurements from thewireless device. The mobility measurements may be performed as in any ofsteps S106 a, S106 b, S106 c above. The RAN node 11 a may then beconfigured to, in an optional step S210, determine a serving beam fromthe set of transmission beams for the wireless device 13 based on thereceived information.

Further, when the serving RAN node 11 a decides on a beam switch, it maysignal identity information, such as the cell ID and/or beam ID for thetarget beam to the WD 13. The WD 13 may then use stored synchronizationparameters for the target beam when receiving data on the serving beam,as in step S120; hence no additional coarse synchronization proceduresor synchronization signaling is needed for the beam switch.Particularly, the RAN node 11 a may be configured to, in an optionalstep S212, transmit identity information of the serving beam to thewireless device 13; and in an optional step S214, transmit data to thewireless device 13 using the serving beam.

Referring back to FIG. 1, WD 13 in region 12 a has an ongoing connectionwith RAN node 11 a on transmission beam 15 a. No pilots are transmittedcontinuously, indicated by the dashed lines for the remainingtransmission beams 15 b-f. RAN node 11 a determines that beam switch isnecessary, based on measurements of the current connection quality forthe serving beam 15 a. These measurements are e.g. measurements ofreceived quality (CQI). Based on e.g. the WD position [x1, y1] or thecurrent transmission beam 15 a, RAN node 11 a selects a set of candidatetransmission beams. If some of the candidate transmission beams belongto RAN node 11 b, RAN node 11 a sends a message to RAN node 11 b toactivate downlink synchronization and reference signals for thosetransmission beams. Alternatively RAN node 11 a could send the WDposition[x1, y1] to RAN node 11 b and RAN node 11 b could decideautonomously which candidate transmission beams to activate. RAN node 11a also informs the WD) 13 to start searching for the MRS/TSS signalsaccording to a supplied list of beam IDs. RAN node 11 a and/or RAN node11 b then transmits TSS/MRS in downlink on the candidate transmissionbeams. The WD 13 then synchronizes and measures on the transmissionbeams and reports the measurement results to RAN node 11 a. RAN node 11a may then determine to perform a beam switch based on the measurementreports. The herein disclosed beam ID list mechanism (i.e., theutilization of previously stored unique identities) is used to avoidperforming the synchronization every time a mobility measurement for atransmission beam is performed. For example, according to at least someof the herein disclosed embodiments the beam ID) corresponding to eachactivated transmission beam is signaled using control signaling from theserving RAN node 11 a to the WD 13. The beam ID may be unique to thegiven beam configuration (originating RAN node, beamforming/precodingparameters, etc.) within some geographical area and it may containinformation at least about the TSS/MRS signals used for synchronization.For the WD 13 to also know which RAN node the transmission beam(s)belongs to, the cell ID could also be provided with the beam ID.

In summary, at least some of the herein disclosed embodiments describe aprocedure to reduce WD) complexity in a communications network to withbeam forming of the downlink channel where there is no continuoustransmission of mobility synchronization and pilot or reference signals.This is achieved by denoting the transmission beams with uniqueidentities, such as beam IDs and cell IDs. Mobility synchronizationmeasurements on the transmission beams may be stored in lookup tableindexed with the beam ID and cell ID. For data transmission to the WD13, the RAN node may inform the WD 13 of the beam ID and cell ID beforetransmitting on the transmission beam The WD 13 may then use storedsynchronization parameters for reception on these transmission beams.

The inventive concept has mainly been described above with reference toa few embodiments. However, as is readily appreciated by a personskilled in the art, other embodiments than the ones disclosed above areequally possible within the scope of the inventive concept, as definedby the appended patent claims.

The invention claimed is:
 1. A method for handling mobilitysynchronization measurements, the method being performed by a wirelessdevice, the method comprising the steps of: receiving, from a radioaccess network node, an indication to perform mobility measurements on aset of narrow transmission beams, wherein the set of narrow transmissionbeams to be measured is indicated by a shared unique identity, andwherein each of the narrow transmission beams has increased signalstrength in a beam direction; prior to performing mobility measurementson the set of narrow transmission beams, checking whether said sharedunique identity has previously been stored by the wireless device, andwhen said shared unique identity has previously been stored by thewireless device: performing mobility measurements on the set of narrowtransmission beams based on previously stored synchronizationinformation of the set of narrow transmission beams, wherein saidsynchronization information is identified by said shared uniqueidentity.
 2. The method according to claim 1, further comprising, whensaid shared unique identity has not previously been stored by thewireless device: performing mobility measurements on the set of narrowtransmission beams to determine synchronization information of the setof narrow transmission beams; and storing said shared unique identityand said synchronization information of said mobility measurements. 3.The method according to claim 1, further comprising: receiving a beamswitch command from a radio access network node serving the wirelessdevice, the beam switch command comprising a target beam identity;checking whether said target beam identity corresponds to any sharedunique identity having previously been stored by the wireless device,and when said target beam identity corresponds to any shared uniqueidentity having previously been stored by the wireless device:retrieving stored synchronization information corresponding to saidshared unique identity; and receiving data transmission using theretrieved synchronization information.
 4. The method according to claim1, wherein said shared unique identity identifies at least one of aradio access network node and a transmission point from which the set ofnarrow transmission beams was transmitted.
 5. The method according toclaim 1, wherein said shared unique identity is represented by asequence of binary digits, and wherein identities of single narrowtransmission beams in said set of narrow transmission beams share atleast a subset of said sequence of binary digits.
 6. The methodaccording to claim 1, wherein said synchronization information isdetermined from synchronization signals transmitted in the set of narrowtransmission beams.
 7. The method according to claim 1, wherein saidsynchronization information comprises at least one of a time offset tostart of a first symbol of a first frame relative an internal clock ofthe wireless device, and a frequency offset to relative a referencefrequency used by the wireless device.
 8. The method according to claim1, further comprising, when said shared unique identity has notpreviously been stored by the wireless device: performing mobilitymeasurements on the set of narrow transmission beams to determinesynchronization information of the set of narrow transmission beams,wherein said mobility measurements are based on previously storedsynchronization information of another set of narrow transmission beams,and wherein said previously stored synchronization information isidentified by a shared unique identity of said another set of narrowtransmission beams.
 9. The method according to claim 8, wherein saidpreviously stored synchronization information of said another set ofnarrow transmission beams is used to define initial parameters to beused during said mobility measurements on the set of narrow transmissionbeams.
 10. The method according to claim 1, wherein said mobilitymeasurements further are based on reference signals transmitted in theset of narrow transmission beams.
 11. The method according to claim 1,further comprising: receiving, while in idle mode, broadcastedinformation; and updating previously stored synchronization informationbased on said broadcasted information.
 12. The method according to claim1, further comprising: transmitting information of said mobilitymeasurements to a radio access network node.
 13. A wireless device forhandling mobility synchronization measurements, the wireless devicecomprising a processing unit, the processing unit being configured to:receive, from a radio access network node, an indication to performmobility measurements on a set of narrow transmission beams, wherein theset of narrow transmission beams to be measured is indicated by a sharedunique identity, and wherein each of the narrow transmission beams hasincreased signal strength in a beam direction; prior to performingmobility measurements on the set of narrow transmission beams, checkwhether said shared unique identity has previously been stored by thewireless device, and when said shared unique identity has previouslybeen stored by the wireless device: perform mobility measurements on theset of narrow transmission beams based on previously storedsynchronization information of the set of narrow transmission beams,wherein said synchronization information is identified by said sharedunique identity.
 14. The wireless device according to claim 13, whereinthe processing unit is further configured to, when said shared uniqueidentity has not previously been stored by the wireless device: performmobility measurements on the set of narrow transmission beams todetermine synchronization information of the set of narrow transmissionbeams; and store said shared unique identity and said synchronizationinformation of said mobility measurements.
 15. The wireless deviceaccording to claim 13, wherein the processing unit is further configuredto: receive a beam switch command from a radio access network nodeserving the wireless device, the beam switch command comprising a targetbeam identity; check whether said target beam identity corresponds toany shared unique identity having previously been stored by the wirelessdevice, and if-se when said target beam identity corresponds to anyshared unique identity having previously been stored by the wirelessdevice: retrieve stored synchronization information corresponding tosaid shared unique identity; and receive data transmission using theretrieved synchronization information.
 16. The wireless device accordingto claim 13, wherein said shared unique identity identifies at least oneof a radio access network node and a transmission point from which theset of narrow transmission beams was transmitted.
 17. The wirelessdevice according to claim 13, wherein said shared unique identity isrepresented by a sequence of binary digits, and wherein identities ofsingle narrow transmission beams in said set of narrow transmissionbeams share at least a subset of said sequence of binary digits.
 18. Thewireless device according to claim 13, wherein said synchronizationinformation is determined from synchronization signals transmitted inthe set of narrow transmission beams.
 19. The wireless device accordingto claim 13, wherein said synchronization information comprises at leastone of a time offset to start of a first symbol of a first framerelative an internal clock of the wireless device, and a frequencyoffset to relative a reference frequency used by the wireless device.20. The wireless device according to claim 13, wherein the processingunit if further configured to, when said shared unique identity has notpreviously been stored by the wireless device: perform mobilitymeasurements on the set of narrow transmission beams to determinesynchronization information of the set of narrow transmission beams,wherein said mobility measurements are based on previously storedsynchronization information of another set of narrow transmission beams,and wherein said previously stored synchronization information isidentified by a shared unique identity of said another set of narrowtransmission beams.